The present invention relates to a channel switching system, and more particularly to a channel switching system used in a digital radio communication system having two or more standby channels.
There are many instances where radio communication systems are configured as regular/standby channel systems provided with one or more standby channels in order to relieve break or interruption of the regular channel which may be caused by fading.
Ordinarily, digital radio communication systems which have adopted the regular/standby channel system function not only to effect channel switching using coaxial switches but also to effect synchronizing switching [as disclosed in the Japanese patent publication No. 143850/80 (Tokkaisho No. 55-143850)] using a transmitting switching circuit comprising electronic circuits provided on the transmitting side and a synchronizing switching circuit provided on the receiving side, thus to prevent occurrence of code errors due to instantaneous interruption at the time of channel switching.
In the regular/standby system, a test signal is caused to be transmitted via the standby channel placed in standby condition to detect, on the receiving side, the test signal which has been transmitted, thereby to monitor communication quality of the standby channel.
In most cases, the conventional regular/standby channel systems used in the digital radio communication systems had employed N to 1 (N:1) system having one standby channel with respect to N regular channels. However, according as the requirement for channel reliability has increased, N:2 regular/standby systems have been recently proposed.
In the digital radio communication system having two or more standby channels, two cases are conceivable in connection with the number of standby channels placed in standby condition. First case is that two or more standby channels are in standby condition. Second case is that only one standby channel is in standby condition. In the prior art, there has not been a channel monitoring system which always monitors the communication quality of each standby channel placed in standby condition in accordance with the above two cases.